Improvements in the design of three-way catalysts which are used to control vehicle emissions have led to the increased use of cerium oxide as an active component. One of the results of increasing the cerium oxide content has been the increased emission of H.sub.2 S to undesirable levels. Government agencies at present do not regulate H.sub.2 S emissions from vehicles, but unusually high H.sub.2 S emission is considered to be undesirable, and in some cases has resulted in warranty replacement.
Several strategies have and continue to be employed to lower H.sub.2 S emission to acceptable levels. The most effective of these strategies involves the incorporation of Ni in the catalyst which reacts with H.sub.2 S in rich exhaust, storing sulfur as NiS and releases sulfur in lean exhaust as SO.sub.2. The European Community has expressed concern about the use of Ni in automobile catalysts due to its toxicity, thus an alternative material having comparable activity is desired. Other strategies that have been proposed or demonstrated involve costly hardware additions, the use of other toxic materials, and treatments to the catalyst which have unknown effects on its durability.
This invention involves the improvement of activity of TiO.sub.2 and H.sub.2 S decomposition. The number of active surface sites can be increased by generating a high surface area rutile TiO.sub.2 powder using a nanophase particle synthesis method. This form of nanophase TiO.sub.2 as prepared is also deficient in oxygen, and thus contains a significant number of defect sites. The number of defect sites contributes to the high activity.
The technology involving the synthesis of nanophase particles is being evaluated as a way to synthesize precursor ceramic powders which can be pressure-molded to form ceramic parts having improved physical properties. This technology, however, has not yet been explored as a method for synthesizing catalytic materials.